If you guys want to lose weight and get good cardio FAST(also good leg workout and even your arms will feel it this is such a crazy work-out) I will tell you the system I just setup one day that works great. This works best with a treadmill just because of the nature of it, but you can do it running around. Okay start off with a walk until you notice your heart pumping a bit, then go to a slow jog, continue the jog until cannot sing but can talk. Then sprint as hard as you can as fast as you can for as long as you can until you feel like you are going to die, then drop back down to a very slow jog until you can talk again and aren't panting like mad, once that has happened sprint as long as hard as you can again until you cannot any longer, then drop back down to a jog, when you can talk again and aren't panting do one more intense sprint and then drop down to a jog again and then after you calm down go to a walk until your temp is down and you feel relaxed. In pretty much any exercise the key is to do as much as you can, take a break, then repeat.
For muscles here is an exercise that requires no weights but a pullup bar is suggested. The best thing to do is start with pullups, what you want do do is do 1 pullup, take a 20 second break, do 2 pullups, take a 20 second break, continue until the highest number you can possibly do, then you want to climb back down. For example I can do 1 pullup, then 2 pullups, then 3 but at 3 I cannot do any more, so I go back down and do 2, and then 1. Do the same for pushups but do it in multiples of 2 or 3, for example: 2 4 6 8 10 8 6 4 2. Keep in mind on pullups and pushups form is more important than anything, and also on pushups do them nice and slow, it won't do you any good to slam to the floor and rush back up and try to do 20 in 5 seconds. If you are doing pullups and you have to squirm and kick and flop around to get up, you aren't doing any good. Next work-out you can do is dips, skull-crushers are better than dips for triceps but not everyone has a curl bar handy, look up dips and skull-crushers if you don't know what they are. Finish off with crunches in the form of 10-20-30-20-10.
Do the cardio exercise 5 days a week, it can be executive days, but do NOT do it 7 days a week. For the second exericse start out at 2 days a week as far apart as possible, definitely do not do it every day, but eventually you can do it every other day. Get lots of protein and as much water as possible and take vitamin supplements and you should be fine, it is preferred to do 5 meals a day but I do 3 meals a day.